Hmmmm....
It should play smoothly. I, of course, watched it - in full screen. It's sharp and judder-free. I just looked again in 480 p, and it was clear and sharp.
I don't really know anything about YouTube. I wonder if you computer's video card is up to speed. I use a MacBook that's about 1 year old, and have not seen what you describe.
The original video was shot in 1080 p, but my imovie editing program couldn't handle it, so it converted it to the next step down (760p ?).
I just spoke to Emmanuel, who was at Retromobile earlier this week. We will do a video of his car getting "the treatment". It's still in Primer at the metalshop, so it's not too late to do a video showing the car in the "early" stages of restoration.
Considering how much effort has gone into Emmanuel's car, it's very instructive to consider going "all the way" from the beginning. There are no shortcuts - previous "restorations" have all been revealed. His car will be better-than-new by a considerable margin when he's done.